It has been usual to package paint in built-up cans, either with or without a handle, having the top closed by a lever lid. Such cans require a substantial amount of fabrication and therefore are relatively expensive.
More recently, paint has to some extent been packaged in containers, which may be referred to as pots or pails, which are moulded from plastics material. This enables substantial reduction of the amount of fabrication required because the bottom and wall of the container can be moulded in a single piece, the lid being the only part which has to be manufactured and applied separately. However, in order to mould the container body in a single piece it has been necessary to leave the inner wall of the container substantially unobstructed so as to enable withdrawal of the mould core from the inside of the container upon completion of the moulding.
When containers are transported along a filling line, to be filled with paint, they are subjected to a certain amount of irregular movement so once the container is filled to a level close to its top there is a tendency for paint to be spilled or slopped over the edge of the container. This is not a significant problem in the usual built-up cans with a lever ring, because the inwardly projecting lever ring tends to prevent paint slopping over the edge of the can. It is, however, a substantial problem when plastic containers are used and attempts to solve it have involved either modifying the filling lines so as to produce less irregular movement of the container, or to employ an over-sized container which will not need to be filled so close to its top, but which of course involves waste because the container has to be made larger than is really necessary to contain the desired amount of paint.